Various properties are required for a ball such as a basketball, a handball, a rugby ball, or an American football. For example, surface abrasion resistance at high level is required for a surface material subjected to repeated rubbing or collision with a hand, a floor, or the like. Further, in a case where a ball is brought into direct contact with a hand, soft cushioning property is required for reducing impact on fingertips in catching of the ball.
Various processes have been proposed heretofore as the process for obtaining a sheet material exhibiting the excellent cushioning property as the surface material of a ball and a leather-like appearance and feel as the taste.
For example, there are proposed: a leather-like sheet at least including 4 layers of a nonporous elastic polymer layer (first layer), a porous elastic polymer layer (second layer), a layer formed of an elastic polymer and a nonwoven fabric (third layer), and a nonwoven fabric layer (fourth layer); and a ball formed of the leather-like sheet (see Patent Document 1). However, in a method of Patent Document 1, the first and second layers were formed by using elastic polymers each having durability for practical use to provide a ball which had insufficient cushioning property and which could not be suitably used as a ball for sports such as a basketball.
Further, in addition to cushioning property, there is proposed, as a leather-like sheet excellent in the three dimensional feel, synthetic leather having a transparent nonporous layer containing polyurethane as a main ingredient laminated on a surface of a base fabric covered with a polyurethane layer and having a pattern of protrusions and depressions. The synthetic leather has an air layer between the depressions and the nonporous layer, and a total area of bonding parts between the protrusions and the nonporous layer accounts for 50 to 90% of a surface area of the synthetic layer (see Patent Document 2). However, even in Patent Document 2, a ball having both cushioning property and durability for practical use and used as a ball handled by a hand such as a basketball has not yet been obtained.
A material for balls absorbing sweat in which a coating layer of a polyurethane coagulated in accordance with a wet process is laminated to the surface of a fibrous material comprising a polyurethane, pluralities of protrusions and depressions disposed between the protrusions are present on the surface of the coating layer, and the side face of the protrusions has an opening, is proposed (see Patent Reference 3). However, dirt tends to be attached to the material of Patent Reference 3. The non-slipping effect extremely decreases after a long use due to accumulation of dirt, and the material cannot be used practically. The soft cushioning property is not satisfactory, either.
Further, there is proposed a basketball having numerous polygonal recesses on an outer surface (see Patent Document 4). However, such polygonal recesses cause a ball formed of a sheet containing a base fabric to have poor softness, cushioning property, and feel. Further, the ball has problems in that abrasion resistance in collision with a ground is reduced and that a ball surface gets dirty easily.
In addition, there is proposed a basketball having numeral specific dimples on an outer surface (see Patent Document 5). According to Patent Document 5, the dimples have a height difference between projections and recesses of 200 to 500 μm, a vertical projected area of each of adjoining recesses of 79 to 314 mm2 (diameter of 10 to 20 mm), and an average distance between the recesses of 8 to 16 mm ( 5/16 to ⅝ inches). However, such large dimples cause a ball formed of a sheet containing a base fabric to have problems such as reduced abrasion resistance, and poor cushioning property and non-slipping property.
Development of a sheet material exhibiting the soft cushioning property of a level higher than that heretofore exhibited in combination with the abrasion strength of the surface and the non-slipping property sufficient for the surface material of a ball for a ball game has been desired.    [Patent Document 1]: Japanese Patent Application Laid-Open No. 2000-102629    [Patent Document 2]: Japanese Patent Application Laid-Open No. Heisei 11 (1999)-93081    [Patent Document 3]: The U.S. Pat. No. 6,024,661    [Patent Document 4]: The U.S. Pat. No. 4,991,842    [Patent Document 5]: The U.S. Pat. No. 5,518,234